1.0 Field of the Disclosure
The disclosure is directed generally to a method and apparatus for tunable notch filters and, more particularly, to a method and apparatus for microwave tunable notch filters, tunable oscillators and tunable filters, and the like, employing Yttrium Iron Garnet (YIG) spheres.
2.0 Related Art
Yttrium Iron Garnet (YIG) filters may include YIG tuned band pass or YIG tuned band reject filters. YIG tuned band reject filters may be know also as YIG tuned notch filters. A fixed tuned non-YIG notch filter is used throughout the realm of electronics. For example, a non-YIG notch filter might be used to block data noise in household digital subscriber line (DSL) systems. Also, a non-YIG notch filter may also be used as a fixed frequency filter in sophisticated microwave systems to block an unwanted high power signal while passing another signal at a close frequency.
YIG tuned notch filters serve a similar purpose in the microwave realm, e.g., about 500 MHz to about 50 GHz. A basic difference, however, is the ability if a YIG tuned notch filter to tune over a wide frequency range and not just reject a “fixed” band of frequencies, as occurs in fixed tuned non-YIG notch filter, for example. In one aspect, it is this frequency agility of YIG tuned filters that make this technology advantageous and appealing.
In a military application, such as a self-protection jammer, for example, the YIG tuned notch filter may be part of a system that protects the aircraft's surveillance receiver from being overloaded or damaged by the airplane's own high power fire control radar, and since the fire control radar may be “hopping around” to different frequencies, the YIG notch filter may be an ideal protection device since, in turn, it can be tuned to these frequencies and jam a high power signal.
A notch filter, fixed tuned or YIG tuned has both a pass band and a stop band or notch. The pass band is typically very wide and is the band over which the input RF-signal may pass with the lowest possible attenuation. The stop band (the notch) is typically very narrow, relative to the pass band, and in the case of a YIG tuned notch filter, the frequency range over which the notch tunes may or may not be coincident with the pass band range, but will always be within the pass band tuning range.
Accordingly, there is a need for a better technique for providing a YIG tuned notch filter in which the minimum rejection bandwidth increases while the maximum 3 dB Notch bandwidth over the tuning band decreases.